The invention relates to a vehicle brake comprising a housing, a brake piston, which is accommodated in the housing and on which a brake lining is fitted, and a blocking device, wherein the brake piston is displaceable in the housing by means of an actuating device and wherein the brake piston is securable relative to the housing by means of the blocking device.
Such a vehicle brake is known for example from the European patent EP 0 551 397, and corresponding U.S. Pat. No. 5,148,894 A1, both of which are incorporated by reference herein in entirety. With this vehicle brake, in a service braking situation, i.e. when a brake disc coupled to a vehicle wheel is to be braked to decelerate the vehicle wheel, a brake piston is displaced relative to the housing and pressed against the brake disc by feeding hydraulic fluid into the fluid chamber. The brake force then exerted on the brake disc is dependent upon the magnitude of the hydraulic pressure prevailing in the fluid chamber. At the end of the service braking situation, hydraulic fluid is discharged from the fluid chamber, thereby allowing the brake piston with its brake lining to move away from and release the brake disc. In a parking braking situation, in which a vehicle equipped with such a brake is to be prevented from unintentionally rolling away by firmly clamping the stationary brake disc against unintentional rotation, in this vehicle brake first the brake piston is again fed towards and pressed against the brake disc by feeding hydraulic fluid into the fluid chamber. Then a motor-driven blocking rod is displaced inside the housing and brought into contact with the brake piston. The blocking rod is supported by a self-locking thread pairing in the housing. The effect achievable thereby is that the blocking rod under the action of axial forces is blocked in its axial position. This effect is utilized to block the brake piston in its brake application position. After the brake piston has been contacted by the blocking rod, hydraulic fluid may be discharged from the fluid chamber, wherein the blocking rod holds the brake piston in its braking position. The hydraulic fluid circuit is therefore relieved and the parking braking function of the vehicle brake is activated. To cancel the parking braking function, the fluid chamber is filled anew with hydraulic fluid until the hydraulic pressure prevailing therein is high enough for the brake piston to release the blocking rod. The blocking rod may then be displaced mechanically into its basic position. The hydraulic fluid is subsequently discharged from the fluid chamber, with the result that the brake piston may readopt its braking-effect-free basic position. For displacement of the actuating rod, according to this patent an electromotive drive is required, thereby lending the entire arrangement a relatively complicated construction. The required electric motor is moreover an additional load on the electrical system of a motor vehicle.